On Tue, 08 Apr 2025, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limoncie...@amd.com>
>
> Currently userspace software systemd treats `brightness` and
> `actual_brightness` identically due to a bug found in an out of tree
> driver.
>
> This however causes problems for in-tree drivers that use brightness
> to report user requested `brightness` and `actual_brightness` to report
> what the hardware actually has programmed.
>
> Clarify the documentation to match the behavior described in commit
> 6ca017658b1f9 ("[PATCH] backlight: Backlight Class Improvements").
>
> Cc: Lennart Poettering <lenn...@poettering.net>
> Cc: richard.pur...@linuxfoundation.org
> Link: https://github.com/systemd/systemd/pull/36881
> Signed-off-by: Mario Limonciello <mario.limoncie...@amd.com>
> ---
> Documentation/ABI/stable/sysfs-class-backlight | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/ABI/stable/sysfs-class-backlight
> b/Documentation/ABI/stable/sysfs-class-backlight
> index 6102d6bebdf9a..909cacde85041 100644
> --- a/Documentation/ABI/stable/sysfs-class-backlight
> +++ b/Documentation/ABI/stable/sysfs-class-backlight
> @@ -26,7 +26,9 @@ Date: March 2006
> KernelVersion: 2.6.17
> Contact: Richard Purdie <rpur...@rpsys.net>
> Description:
> - Show the actual brightness by querying the hardware.
> + Show the actual brightness by querying the hardware. This
> + takes into account other factors besides the value programmed
> + for 'brightness' and may not match the value in 'brightness'.
Which factors? Under what circumstances may the values not match?
> Users: HAL
>
> What: /sys/class/backlight/<backlight>/max_brightness
> --
> 2.43.0
>
--
Lee Jones [李琼斯]
